measure.

FIRST SENTENCE OF THE FIRST MOVEMENT OF THE TWELFTH SONATA.

No difficulty will be found in following the cadences and endings of
this sentence, the long-drawn out lines of which give an impression of
repose and tranquillity. Two more excellent examples of 16 measure
sentences may be found in the Adagio of the Fifth Sonata, and in the
Scherzo of the Third; the latter movement is remarkable for the
polyphonic treatment of the opening motive.

Although the three types of sentence just studied, _i.e._, of 8, 12
and 16 measures are the normal ones, and would include a majority of
all sentences--especially in smaller works--in large compositions
there would be an unendurable monotony and rigidity were there
invariably to be cadential pauses at every 4th measure. We all know
the deadening effect of poetry which has too great uniformity of
metric pattern; and verses of "The boy stood on the burning-deck" type
are considered thoroughly "sing-song." It is obvious that elasticity
may be gained, without disturbing the normal balance, by expanding a
sentence through the addition of extra measures, or contracting it by
the logical omission of certain measures or by the overlapping of
phrases.

The simplest and most common means of enlarging a sentence is by the
extension, or repetition, of the final cadence--that effect which is
so frequent in the chamber and symphonic music of Haydn, and which has
its comic manifestation in the so-called "crescendo" of the Rossini
Operatic Overture.[60]

[Footnote 60: For a burlesque of this practise see the closing
measures of the Scherzando movement of Beethoven's Eighth Symphony.]

[Music: HAYDN: _Quartet, op. 74, No. 2_]

As Haydn was an important pioneer in freeing instrumental structure
from dependence on the metre of words, his periods are always clearly
organized; the closing measures of this example seem, as it were, to
display a flag, telling the listener that the first breathing-place is
reached. Very often both the fore-phrase and the after-phrase have
cadential prolongations, an example of which may be found in Haydn's
Quartet, op. 71, No. 3. The two following illustrations (the first
movement of Beethoven's Fifth Sonata and the third movement of the
Fourth) furnish remarkable examples of extended 16 measure sentences;
each sentence being normal and symmetrical at the outset and then, as
the fancy of the composer catches fire, expanding in a most dramatic
fashion.